Add support for retrying failed requests

[dcu]

What would you like to be added?

429 and 5XX errors should be retried

Why is this needed?

it improves the UX otherwise the dev would have to check the response and implement retries every time this library is used

Anything else we need to know?

[dcu]

a way to fix this is using https://github.com/hashicorp/go-retryablehttp like this:

	retryClient := retryablehttp.NewClient()
	retryClient.RetryMax = 15
	standardClient := retryClient.StandardClient()

	tp := jira.BasicAuthTransport{
		Username:  username,
		APIToken:  password,
		Transport: standardClient.Transport,
	}